The present invention relates to an information recording apparatus, an information recording method and an information recording system for recording information on an optical disc serving as a recording medium.
In recent years, in the field of information recording apparatuses, write-once optical discs, such as CD-R discs, and rewritable optical discs, such as CD-RW discs, have been commercialized as recording media. Recently, by shortening the wavelength of a semiconductor laser serving as a laser light source, by decreasing the spot diameter of a high-NA objective lens having a high numerical aperture, by employing thin substrates and by taking other measures, large-capacity optical discs, such as DVD-R, DVD-RW, DVD-RAM discs, have been used in information recording apparatuses.
For example, recording information on a DVD-R disc, one of recording media (dyestuff-based recording media) having a dyestuff recording layer, is carried out by a mark-edge recording system for recording information at the leading and trailing edges of marks on the recording medium. In the recording on this kind of large-capacity optical disc, a pulse control system for adjusting the intensity of the laser depending on the quality of an optical disc to be used in consideration of improper mark formation due to insufficient thermal storage and cooling speed of the recording medium has been put into practical use. This pulse control system carries out ON/OFF control of the laser at short intervals to adjust the intensity of the laser. In this pulse control system, a laser emission waveform rule (hereafter referred to as a write strategy) wherein multiple pulses in a pulse train comprising the combination of a head heating pulse and a plurality of following continuous heating pulses has been proposed. In addition, as another pulse control system, a method wherein the pulse width of the head heating pulse is changed depending on the length of a mark and the length of a space immediately before or after the mark has also been proposed.
When recording on a dyestuff-based recording medium or a recording medium based on a phase-change recording system, recording conditions differ depending on ambient temperature and the type of the recording medium, and the optimal write strategy at that time also differs. Japanese Patent Unexamined Publication No. 2000-207742 discloses an information recording method for determining a write strategy being different at every recording time.
FIG. 18 is a block diagram showing the configuration of an information recording apparatus disclosed in Japanese Patent Unexamined Publication No. 2000-207742. FIG. 19 is a block diagram showing the configuration of a controller in the information recording apparatus of FIG. 18.
In the conventional information recording apparatus, when determining a write strategy, for example when determining emission power (recording power) at the time of recording, asymmetry occurring in a signal at the time of reproduction of a recorded area is adjusted, and the power is determined. In addition, when determining an emission waveform rule, jitter occurring in the signal at the time of reproduction of the recorded area is adjusted, and the rule is determined. Furthermore, in the conventional information recording apparatus, with respect to asymmetry and jitter, a predetermined pattern (test pattern) formed of marks and spaces having 3 times (3T) to 11 times (11T) and 14 times (14T) the period (T) of a channel clock serving as a data extraction clock signal is written (recorded) on trial at several kinds of recording power levels, and data at each recording power level is measured by using the reproduced signal of the predetermined pattern.
FIG. 20 is a waveform diagram showing the measured values of asymmetry (a) and jitter (b) in the conventional information recording apparatus. The upper waveform in FIG. 20(a) indicates measured asymmetry [%], and the lower waveform indicates the position of a focal point [μm]. Furthermore, the upper waveform in FIG. 20(b) indicates measured jitter [%], and the lower waveform indicates the tilt [deg] of an optical disc. The waveforms in FIG. 20 are based on measured values obtained when the optical disc carries out one rotation.
As shown in FIGS. 20(a) and (b), in the reproduced signal of the test pattern, the asymmetry and jitter values change because of the influence of stress during recording and reproduction, for example defocusing, that is, the displacement of the focal point, the tilt of the disc in the tangential direction of its track, etc.
Since the asymmetry and jitter values change as shown in FIG. 20, in the conventional information recording apparatus, the respective average values of the asymmetry and jitter values are calculated, and by using the calculated average asymmetry and jitter values, recording power and an emission waveform rule are determined. In the conventional information recording apparatus, in order to remove the AC components of the stress caused by the rotation of the disc, the asymmetry and jitter values are detected for one rotation of the disc, and by using the average values of the asymmetry and jitter values, a write strategy for the disc is determined.
Hence, in the method of determining a write strategy (laser emission waveform rule) in the conventional information recording apparatus, it is necessary to carry out trial writing many times in order to obtain optimal recording conditions. For example when data recording for one rotation is carried out for one condition, it is necessary to use a dozen or so tracks as a learning area for one-time learning. Furthermore, a write-once optical disc, such as a DVD-R disc, has a constraint that recording cannot be carried out on tracks recorded once and areas reserved for adjustment is scarce. Hence, in the conventional information recording apparatus, when responding to incremental writing, it is necessary to make the one-time learning area used for determining a write strategy (laser emission waveform rule) as small as possible.
In the conventional information recording apparatus, for example in an optical disc, such as a DVD-R disc, the area usable as a learning area is a PCA (Power Calibration Area) reserved as an area for writing power adjustment, and the PCA has 7056 sectors. In the conventional information recording apparatus, an information recording method for determining the above-mentioned write strategy by using the 7056 sectors of the PCA has been used. However, in this single area, sufficient learning for determining the write strategy cannot be carried out. Even if trial writing is carried out while changing only the parameters greatly contributing to the determination of the write strategy, sufficient learning times cannot be obtained in the conventional information recording apparatus, whereby no appropriate write strategy can be determined.